Atomizer wheels of the type used for the atomization of slurries of highly abrasive materials are comprised of a hub secured to a rotating shaft, a wheel bottom connected to the hub, a cylindrical side wall connected with the wheel bottom and a cover plate to form a bowl-shaped feed supply chamber. The feed supply communicates with an inlet in the cover plate for a liquid suspension or slurry to be atomized. The side wall typically has at least one row of openings fitted with nozzles frequently in the form of bushings which eject droplets of the suspension or slurry from the bowl-shaped chamber.
The process of spray drying liquids and solids in liquid suspensions is critically dependent upon the means used to form small droplets of the feed material so as to facilitate vaporization of the liquid carrier. For purposes of the present invention, the term atomization is used to describe the formation of small droplets.
Various liquids and various solids in a liquid suspension require specific handling in a spray drying process. The specific design and operation of an atomizer wheel are critical functional and economic factors in spray drying operations. Atomization of suspensions of abrasive materials has long been recognized as a critical problem in spray drying operations particularly when processing abrasive materials at high wheel loadings. Equipment failure due to the action of the abrasive materials at points of wear on the atomizer wheel interrupts process operation and requires costly equipment replacement.
Various measures have previously been suggested to reduce the undesirable abrasive action in atomizer wheels. U.S. Pat. No. Re 32,064 describes an atomizer wheel comprising an annular chamber provided with a number of conical outlet holes lined with bushings to provide nozzles having their inner ends extending a distance into the interior of the chamber. Each of the outlet holes is lined with a bushing formed of a wear-resistant sintered material.
The use of replaceable steel bushings to seat wear-resistant ceramic linings in a number of ejection apertures or orifices along the circumference of an external wall of an atomizer wheel is described in U.S. Pat. No. Re 30,963. The inner end of the steel bushings and/or the linings project into the annular chamber of the atomizer wheel and the bushings are sealed against the external wall.
U.S. Pat. No. 4,684,065 describes an improved structure wherein each bushing is provided at its inner surface facing the wear-resistant lining with a flat recess permitting the steel bushing to be resiliently deformed without transferring excessive stress to the lining.
U.S. Pat. No. 3,887,133 describes an atomizer wheel comprising a number of ejection orifices and a number of spoke-like projections extending into the annular bowl-shaped space defined by the interior of the wheel.
In U.S. Pat. No. 4,303,200, an atomizer wheel is provided with a number of ejection orifices with each orifice including a bushing having a slit extending part way across the interior end of the bushing. The atomizer wheel described therein is directed to the atomization of non-abrasive solutions and is unsuited for suspensions or slurries of heavy abrasive products.
It is an object of the present invention to provide an atomizer wheel useful for the atomization of highly abrasive materials which has both improved resistance to abrasion, particularly when processing abrasives at high wheel loadings, and provides considerably increased capacity.